HydroClim Minnesota for Early September 2013

A monthly electronic newsletter summarizing Minnesota's climate conditions and the resulting impact on water resources. Distributed on the first Thursday of the month.

State Climatology Office - DNR Division of Ecological and Water Resources, St. Paul
distributed: September 5, 2013

What happened in August 2013:

  • August rainfall totals were below historical averages in most Minnesota counties, except in far northwest and north central Minnesota where monthly totals were somewhat above average. In many communities, especially in east central Minnesota counties, August precipitation totals fell short of long-term averages by two or more inches. Across much of the southern three-quarters of Minnesota, July-plus-August rainfall totals were four to six inches below normal. Rainfall deficits, along with very hot late-August temperatures, led to a rapidly developing drought situation across much of the Midwest.
  • As was the case in June and July, average monthly temperatures for August in Minnesota were quite close to historical averages. Cool temperatures during the first half of the month were counterbalanced by very warm temperatures in the final two weeks of August. Extremes for the month ranged from a high of 99 degrees on the 25th at Wild River State Park (Chisago County), to a low of 31 degrees at Embarrass (St. Louis County) on the 14th. Some low minimum temperature records were set during the first two weeks of August. A number of high temperature records were set in the final week of August.

Where we stand now:

  • Season-to-date precipitation totals are highly variable across Minnesota. Spring and early-summer precipitation totals were ample to excessive in many locations, especially southeast Minnesota. Whereas, precipitation totals from the last week of June through early-September were substantially below average in all but the northernmost counties. The seasonal precipitation map offers a patchwork pattern of values above and below historical normals.
  • The U. S. Drought Monitor, released on September 5, places an area of central Minnesota in the Severe Drought category. Large portions of the rest of the southern two-thirds of Minnesota are rated in the Moderate Drought category. The expansion of the drought areas was due to July-plus-August rainfall shortfalls of four to six inches along with hot late-summer temperatures. The U. S. Drought Monitor index is a blend of science and subjectivity where drought categories (Moderate, Severe, etc.) are based on several indicators.
  • The U.S. Geological Survey and the Minnesota DNR report that stream discharge values are on the low end of the "normal" range at roughly two-thirds of Minnesota's gauging locations. Stream flow values are below the 25th percentile of the historical distribution for many watersheds in northwest, central, east central, and south central Minnesota.
  • Water levels on Minnesota lakes are dropping as is common in the late-summer. In some cases, lake levels in the southern three-quarters of Minnesota are dropping faster than typical seasonal rates due to the dry weather and evaporation demands brought on by hot late-season temperatures.
  • In their September 1 report, the Minnesota Agricultural Statistics Service reported that topsoil moisture was 24% Very Short, 42% Short, 34% Adequate, and 0% Surplus across Minnesota. Subsoil moisture was said to be 18% Very Short and 43% Short. Soil moisture measurements made at two University of Minnesota Research and Outreach Centers in mid-August indicated below-average conditions at these southern Minnesota locations.
  • The potential for wildfires is currently rated by DNR Forestry as Moderate in most Minnesota counties. The fire danger is rated High in some northwest Minnesota counties, and Low in a few north central counties.

Future prospects:

  • The September precipitation outlook indicates equal chances of below-normal, near-normal, or above-normal conditions throughout Minnesota. September precipitation normals range from near two inches in far western Minnesota to around three and one-half inches in eastern sections of the state.
  • The September temperature outlook indicates equal chances of below-normal, near-normal, or above-normal conditions everywhere in Minnesota. Normal September high temperatures are in the mid-70s to start the month, dropping to the low to mid-60s by month's end. Normal lows are in the mid-50s early in the month, falling to around 40 by late September.
  • The 90-day precipitation outlook for September through November offers equal chances of below-normal, near-normal, or above-normal conditions in all but southeast Minnesota. In southeast Minnesota the 90-day precipitation outlook leans towards above-normal conditions. The September through November temperature projection calls for equal chances of below-normal, near-normal, or above-normal conditions in most locations. However, the temperature outlook tilts towards above-normal conditions in northeast Minnesota.
  • The National Weather Service produces long-range probabilistic river stage and discharge outlooks for the Red River, Minnesota River, and Mississippi River basins. These products address both high flow and low flow probabilities.

From the author:

  • As was the case in 2012, mid-summer and late-summer rainfall deficits along with high evaporative demand from warm late-summer temperatures have led to rapidly deteriorating drought conditions. Ample autumn rains will be required to refill the soil moisture profile and to recharge groundwater and surface water systems.

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Greg Spoden, DNR Climatologist

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